Motor housing having simplified cover plate and brush base

ABSTRACT

An end assembly for a miniature motor. The end assembly including a brush base, a pair of brush arms supporting brushes, and a cover plate supporting a rotor bearing. The end assembly fits into an open end of a cylindrical motor housing.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of Provisional ApplicationNo. 60/238,019, filed Oct. 6, 2000, the entire content of which ishereby incorporated by reference in this application.

FIELD OF THE INVENTION

[0002] The invention relates generally to miniature motors used in, forexample, toys; audio and video equipment, and automotive electricalappliances, hand tools and other motor-driven devices. Moreparticularly, the invention relates to an end cover plate and brush basefor a motor casing of a miniature motor.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0003]FIG. 1 is a miniature motor 10 having a metallic cylindricalhousing 12. The housing 12 may be formed of mild steel and have a hollowtubular section 14 and an integral bottom 16. The opposite end 30 of thehousing is open to receive a brush base and cover plate at one end ofthe tubular section. Within the housing are fixed a pair of oppositepermanent magnets 18, each of which have an arc shape to match the innerwall of the housing. The magnets form between them a volume in thehousing for a rotor 20. The rotor includes a cylindrical armature 22coaxially mounted on a rotor shaft 24. The rotor shaft 24 extendsthrough the opposite ends of the housing 12.

[0004] Bearings 26 are mounted to rotatably support the shaft in theends of the housing. The bottom 16 of the motor housing has an integralflange 28, into which is press-fitted a bearing 26 to support one end ofthe rotor shaft 24. The opposite end 30 of the housing has an opencylindrical base which receives a brush base 32 and cover plate 34 whichare assembled together to fit in the open end 30 of the housing.

[0005] The cover plate 34 fits over the base, and the cover plate andbrush base fit into the motor housing. The open edge of the housing iscrimped onto the plate. The cover plate 34 has a flange 36 to support abearing 26 which supports an end of the rotor shaft 24. The flange 36and bearing 26 of the cover plate 34 (when inserted in the motorhousing) are coaxially aligned with the flange 28 and bearing 26 on thebottom section 16 of the motor housing so that the rotor shaft is heldin coaxial alignment with the motor housing 12.

[0006] The brush base 32 supports a pair of brush arms 38 which providean electrical connection between an external electrical contact 40 ofthe motor and the armature 22 of the rotor 20. The brush arms aregenerally strips of copper having a first end fixed to the periphery ofthe brush base 32 and an opposite, free end on which is mounted a brush42. The brush arms are attached to opposite sides of the brush base. Thebrushes on the arms face each other at the axis of the motor. Wheninserted in the housing, the brushes are in slidable contact with thecommutator 44 on the rotor shaft 24. The commutator provides anelectrical contact between the wiring of the armature 22 and thebrushes.

[0007] The external contacts 40 of the brush arms provide directelectrical current (D.C.) through the brushes and the commutator to thewindings in the armature 22. Electrical current flowing through thearmature creates an alternating magnetic field within the housing thatinteracts with the magnetic field of the permanent magnets 18. Thisinteraction of magnetic fields creates a force that rotates the rotor20. This rotation drives the rotor shaft 24 to provide a mechanicalrotational output power source from the rotor. The rotor shaft 24extends through the bottom 16 of the housing to provide a mechanicalpower output to drive a gear box or other device.

[0008] Conventional cover plates 34 are cylindrical discs havingembedded recesses which fit into matching slots in the brush base 32and/or grooves in the end 30 of the housing. Forming a motor platehaving recesses, brush bases having slots and machining the motorhousing to have the grooves needed to match the cover plate and/or baseadds to the complexity and cost of miniature motors. Miniature motorstend to be a relatively-low cost component of toys and other equipment.Accordingly, it is important that manufacturing costs for making thesemotors be minimized.

SUMMARY OF THE INVENTION

[0009] The invention is intended to overcome the problems inherent withprior miniature motors having complicated brush bases, and motor plates.Specifically, the invention relates to a simplified construction of amotor housing, brush base and motor plate.

[0010] The simplified construction features include a motor housinghaving an outer end which has a smooth circular edge, that does notrequire the cutting of slots into the edge. Minimal machining may beapplied to the edge to polish an outer ring of the housing and tomachine a lip to engage the brush base. The brush base also has asimplified construction and formed by injection molded plastic.Moreover, the brush base has several features which facilitate theassembly of the motor housing including a collar and flange that fiteasily into the motor housing to fix the position of the brush baseinside the housing. The cover plate, which may be a simple metal stampconstruction, fits directly onto a planar region of the brush base.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a partial cross-sectional side view illustrating anexample of a conventional miniature motor.

[0012]FIG. 2 is an exploded view of a motor casing, brush base and motorplate.

[0013]FIG. 3 is an end view of a motor casing assembled with a brushbase and motor plate.

[0014]FIG. 4 is a side view of the brush base shown in FIG. 2.

[0015]FIG. 5 is an inside end view of a brush base.

[0016]FIG. 6 is a cross-sectional diagram of the brush base shown alongsection line 6-6 in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

[0017]FIG. 2 shows an exploded view of a motor housing 50, a brush base52 and a motor cover plate 54. The housing 50 is a cylindrical metallicsteel shell having an open end 56 and a closed bottom end 58. Anadvantage of the motor housing 50 is that the open end 56 has a smoothcircular edge which is easily fabricated and does not requirespecialized machining to form grooves, slots or other shapes in theedge. By eliminating the grooves, slots or other shapes at the edge, thecircular edge of the end 56 is a smooth surface, with good roundness.The outer surface of the housing may be formed at ring 60, which extendsapproximately 0.25 inch from the outer edge 56 of the housing.

[0018] The inside surface of the housing includes an annular lip 62,which engages a pair of flange sections 64 of the brush base. Theannular lip is a ring on the inside surface of the housing, adjacent tothe edge 56, and having a diameter slightly greater than the insidediameter of the housing. The ring may have a rounded shoulder at thetransition between the ring and the rest of the inside surface (having asmaller diameter) of the tubular housing. A rounded shoulder may providea better grip on the flange 64 of the base holder, which is entirely ina plane normal to the axis of the housing. The formation of a smooth andcontinuous edge 56 of the housing having an outer polished ring 60, andan inner lip 62 with good roundness is relatively simple andinexpensive.

[0019]FIG. 3 shows the brush base 52 and motor cover plate 54 insertedin the open end 56 of the housing. The brush base and cover plate arecoaxially aligned with the housing. To secure the brush base in thehousing, a crimping tool (not shown) makes small indentations 66 on theouter edge 56 of the casing. These indentations bend inward to the edge56 of the housing to fix the brush base 52 and cover plate 54 to thehousing. The indentations 66 in the housing edge 56 are aligned with thebase and the cover plate to hold both the base and plate in the housing,and to locate the relative position between the brush base and housingwithout any rotation. The outer diameter of the brush base 52 slidesinside the inside diameter (beyond the lip 62) of the housing 50 by wayof an interference fit. The flanges 64 of the base slide in the housinguntil they engage the lip 62. The lip has a diameter slightly larger,e.g., by one or more tenths of an inch, than the inside diameter of thehousing. The flange and lip engagement prevents the brush base fromsliding further into the housing. The engagement of the flanges 64 andlip 62, and the crimping 66 of the edge of the housing onto the brushbase and cover plate, the brush base is held securely within the motorcasing 50.

[0020]FIG. 4 shows a side view of the brush base 52. The base includesan annular collar 70 that has an outside diameter substantially the sameas the inside diameter (below the lip 62) of the housing 50. The brushbase is formed of a plastic material having relatively high rigidity andstrength, and a large dielectric constant to provide electricalinsulation. The collar may include a pair of opposite vertical slots 73to receive a grounding element to the housing when assembled. The slotmay extend substantially the height of the collar, except for the flange64 continues across the slot. These slots 73 may not be necessary forsome motors. The outer end 72 of the base 52 includes a recessed centerplanar section 74 that provides a platform on which the cover plate 54lies. The planar region 74 has a semi-rectangular opening (76 in FIG. 5)to provide open access through which extends the rotor shaft. To assistwith attaching the motor plate 54 to the brush base 52, the planarregion 74 includes small posts 68 which fit into matching apertures 78in the cover plate. The plate is fitted onto the planar region 64 andsnapped onto the posts 68. To secure the plate, the outer tips of theposts 68 may be press fit to form a rivet-type connection holding theplate onto the brush base.

[0021] The outside end 72 of the brush base also includes a pair ofopposite plateau-flanges 64 that are slightly elevated above the planarregion. Each plateau-flange has an inner straight edge 80 that bordersthe cover plate, and an outer arc-shaped edge that slightly overhangsthe collar 70 of the brush base, e.g., by about a tenth of an inch. Theoverhang of the flange abuts against the lip 62 of the housing, when thebase is inserted in the housing. Thus, the overhang should extend beyondthe collar by approximately the same distance as the width of the lip inthe housing. The flanges are each a relatively thick portion of the baseand include slots through which extend the electrical contacts 82 forthe motor.

[0022] The inside end 84 of the brush base 52 slides into the housing. Apair of magnet posts 86 extend downward from the end 84 of the base andabut against the permanent magnets 18 fixed to the inside wall of themotor housing. These posts 86 insure that the permanent magnets and thebrush base remain properly separated in the motor housing.

[0023]FIG. 5 shows a bottom view of the brush base 52 and FIG. 6 shows across-sectional view of the brush base through section line 6-6. Toprovide structural support for the magnet post 86, a pair of postsupports 88 are formed in the brush base integral with the collar 70.Similarly, an arm support 90 is integrally formed with the collar andprovides a support for a pair of the brush arms 92. The arm base 90includes slots to receive the end of the brush arm, and to provide anelectrical connection with the external connector 82.

[0024] Each brush arm 92 is formed of a highly conductive metal, such ascopper, and extends from the base 52 towards the center of the brushbase. The arm may have a shallow U cross-sectional shape to providestructural rigidity to the arm. At the free end of each arm (towards thecenter of the motor) is attached a conductive brush 94. The arm forms acantilevered beam that holds the brush and biases against thecommutator. The brushes are rotatably and slidably in contact with thecommutator of the motor and provide the electrical connection betweenthe rotor and the external power contacts.

[0025] The brush base 52 is an integral plastic component that isinjection molded. The external connectors 82, brush arms 92 and brushes94 are fastened to the brush base 52 to form a complete component readyfor assembly in the motor. The cover plate 54 is a flat metallic plateeasily formed. As shown in FIG. 3, the plate has a semi-rectangularouter shape, including a pair of opposite straight edges which are inabutting contact with the flanges 64 of the base. The other pair ofedges of the plate are arc-shaped to match the curvature of the open end56 of the motor housing. The plate also includes a center circular plate96 that is slightly raised to provide structural support for the bearingflange 98. This flange supports the rotor bearing 26 and the rotor shaft24.

[0026] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A motor comprising: a cylindrical housing havingan open end with a continuous circular edge and a lip on an insidesurface of the housing; a brush base having an annular collar which fitsinto the open end of the housing, an outside end of the collar includesa recessed planar area and at least one plate adjacent the planarregion, wherein the plates overhang a periphery of the collar and abutsthe lip when the base is inserted in the housing, and a cover platesized to fit on said planar area of the brush base, said plate having anannular flange to support a rotor bearing.
 2. A motor as in claim 1,wherein said brush base further includes a pair of brush arms supportingbrushes.
 3. A motor as in claim 2, wherein the brush base furtherincludes external connectors attached to the brush arms, extendingthrough the base and protruding outwardly from the outside end of thecollar.
 4. A motor as in claim 1, wherein the brush base is formed ofplastic and the plate is metal.
 5. A motor as in claim 1, wherein theplanar area has a post which inserts into apertures of the plate, andthe post is permanently press fit to secure the plate.
 6. A motor as inclaim 1, wherein the annular collar has a circular cross section.
 7. Amotor as in claim 6 wherein the collar has an outer peripheral surfaceform a substantially uninterrupted annular surface.
 8. A motor as inclaim 7, wherein said outer peripheral surface of the collar isinterrupted by a pair of narrow vertical slots in the surface.
 9. Amotor as in claim 1, wherein the cover plate is a semi-rectangular platehaving a raised disk with the annular flange.
 10. A motor as in claim 1wherein the outer peripheral surface includes crimping to hold the coverplate on the brush base.
 11. A motor comprising: a cylindrical housinghaving an open end with a continuous circular edge and a lip on aninside surface of the housing; an annular brush base having a planarsurface area, and a flange extending beyond an annular peripheralsurface of the brush base; a cover plate fitted on the planar surfacearea of the brush base, and wherein the cover plate and brush base arepress fitted into the open end of the housing and the flange of thebrush base abuts against the lip of the housing.